Asphalt-based roof coatings having thick, highly-viscous characteristics have been used for many years to seal joints between roof membranes, join flashings to parapet walls and otherwise repair, seal and protect roof surfaces from exposure to the environment. These roof coating products are typically available in one to five gallon pails for use by homeowners or are available in bulk for use by professional roofing contractors.
Prior art asphalt-based roof coatings typically include asphalt, clay and a surfactant. The asphalt is used as a binder and the clay thickens the composition and provides gelling properties. The surfactant is present to produce optimum wetting and dispersion by reducing the interfacial tension between the asphalt and clay. Additives known as fillers may be included to provide bulk and other properties to the roof coating composition. These asphalt-based coating compositions are an improvement over earlier compositions which include asbestos. The asbestos is added to the composition to provide texture, strength and thixotropic properties to the formulation.
A roof coating composition which is effective for its purpose must have certain characteristics, most of which are a function of the surfactant selected for use in such composition. The roof coating composition must be relatively inexpensive to manufacture (so that it can be competitively priced) because the roof coating industry is intensely competitive. As those experienced in the art are aware, small price differences per unit volume have a significant effect on product sales and can mean the difference between success or failure in the marketplace. The high cost of the surfactant, in particular, makes certain prior art roof coating compositions expensive and places such products at a disadvantage in the marketplace.
The roof coating composition must have the appropriate physical characteristics to properly seal a wide range of roof surfaces and resist degradation when exposed to extreme environmental conditions. The composition must be highly viscous to adequately coat and seal the roof surface and to stay in place at the point of application. Viscosity, of course, refers to the thickness of the composition. Increased viscosity is desirable and indicates that the clay and asphalt constituents are well-dispersed, thereby assuring optimal performance of the composition. In addition to suitable viscosity, the composition should have superior gel stability meaning that the viscosity remains constant between manufacture and application to the roof surface.
While the composition must be viscous and have good gel stability, it should also be easy to manufacture and formulate. The most desired surfactants should be liquid (not solid) so that they can be handled easily and readily mixed with the asphalt and clay without having to apply heat or extraordinary mixing equipment.
The surfactant of the roof coating composition must be robust and capable of dispersing other ingredients and imparting appropriate viscosity to compositions including a wide range of asphalts and clays. Asphalts, in particular, lack uniformity and vary greatly in constituents. Also, as is well known in the roof coating manufacturing industry, asphalts may be oxidized or unoxidized, depending upon the practice of the asphalt manufacturer. Oxidization of the asphalt can greatly affect its characteristics. Inability of the surfactant to disperse a wide range of constituents will result in loss of viscosity and cause premature failure of the composition.
But those are not the only characteristics of a preferred roof coating. Relative freedom from odor, especially offensive odor, and compatibility with composition containers and metal surfaces are others. Freedom from corrosivity may be particularly important if the composition is used for other applications such as automobile undercoatings.
One example of a very-effective prior art asphalt-based roof coating composition is disclosed in U.S. Pat. No. 4,759,799 (Vicenzi). The roof coating composition of the Vicenzi patent includes asphalt, clay and a surfactant. The surfactant is an alkyoxyalkylamine salt, preferably, decyloxypropylamine acetate which is sold by Tomah Products, Inc. of Milton, Wis. under the tradename PA-14 Acetate. Roof coating compositions using the PA-14 acetate surfactant have excellent performance and handling characteristics and are robust. Their premium price reflects the cost of the surfactant.
Another prior art roof coating composition is Redicote CG manufactured by Akzo Chemie of Chicago, Ill. Redicote CG is an asphalt-based roof coating composition and has the disadvantage of having an odor which some consider to be offensive. The odor issue is a particular problem during manufacture of the Redicote CG.
An inexpensive roof coating composition with improved viscosity and gel stability, which is easy to manufacture and apply, which is robust and capable of being used with a wide variety of asphalts and clays and which avoids the disadvantages of prior art roof coating compositions would represent a significant advance in the art.